The present invention relates to an optical film useful in a light diffuser film, polarizing film or the like, and to optical elements using the optical film.
Optical films have been known which comprise a matrix and dispersedly contained therein regions having anisotropy in refractive index and are anisotropic with respect to the scattering of linearly polarized light (see U.S. Pat. Nos. 2,123,902, 5,783,120, 5,825,543, and 5,867,316). In this type of optical film, one of two lights linearly polarized in respective directions perpendicular to each other is forcedly scattered and the other only is caused to pass therethrough. However, there has been a problem that it is difficult to use these optical films in the light diffuser film or viewing-side polarizing film of a liquid crystal display or the like because use thereof in this application results in enhanced backward diffuse reflection and a reduced contrast.
Accordingly, one object of the invention is to provide an optical film which is reduced in diffuse reflection while retaining anisotropy in the scattering of a linearly polarized light and is practically usable in a light diffuser film or viewing-side polarizing film for liquid crystal displays and the like.
Another object of the present invention is to provide an optical element using the optical film.
The invention provides an optical film comprising a light-transmitting resin and dispersedly contained therein minute regions differing from the light-transmitting resin in birefringent characteristics, wherein the difference in refractive index between the minute regions and the light-transmitting resin in a direction perpendicular to the axis direction in which a linearly polarized light has a maximum transmittance, xcex94n1, is from 0.03 to 0.5 and that in the maximum-transmittance axis direction, xcex94n2, is smaller than 0.03, and the diffuse reflectance of linearly polarized light in the xcex94n1 direction is lower than 30%.
The invention further provides: an optical element comprising two or more layers of the optical film, wherein the layers are superposed such that the xcex94n1 directions for any of the layers are parallel to those for the adjacent layers; an optical element comprising a multilayer structure which comprises at least one of a polarizing film and a retardation film and one or more layers of the optical film, an optical element comprising a multilayer structure which comprises a transparent resin plate and., disposed on one or each side thereof, one or more layers of the optical film; and an optical element which comprises one layer of or two or more superposed layers of the optical film and a reflecting layer disposed thereon.
The optical film according to the invention has the following excellent anisotropy in scattering. In the axis direction in which a linearly polarized light has a maximum transmittance (xcex94n2 direction), the linearly polarized light passes through the optical film while satisfactorily retaining its polarized state. In directions (xcex94n1 directions) perpendicular to the xcex94n2 direction, the linearly polarized light is scattered based on the difference in refractive index xcex94n1 between the light-transmitting resin and the minute regions, whereby the polarized state is diminished or eliminated. Based on this anisotropy in scattering, light loss by absorption and heat generation by light absorption can be prevented. In addition, the optical film is reduced in diffuse reflection. Consequently, even when used in the light diffuser film or viewing-side polarizing film of a liquid crystal display or the like, the optical film is less apt to cause a decrease in contrast.